Bacterial wilt, which brings down serious damages to agricultural crops, is known to be a disease that is difficult to prevent. Methods of preventing bacterial wilt thus far developed include mainly a technology aimed at killing Ralstonia solanacearum, pathogen, with antibiotics and the like (Study Reports of Agricultural Experiment Station, Okayama Prefectural Center for General Agriculture, No. 19, p. 29-35 (2001-12)), or a technology aimed at restraining the growth of the pathogen by grafting using a variety that is resistant to the disease as a rootstock (Journal of Phytopathological Society of Japan, Vol. 63, No. 2, p. 83-88 (1997-4)).
However, the method that involves use of antibiotics has a problem that the method gives the pathogen a stress to exist and a microorganism resistant to the stress will appear. On the other hand, the method that involves using a variety that is resistant to the disease as a rootstock takes many troubles and much time and hence tends to be avoided in a large-scale cultivation.
Incidentally, it has revealed that methyl 3-hydroxypalmitate represented by the general formula (I)
functions as a regulator for the pathogenic expression of Ralstonia solanacearum (Flavier, A. B., Clough, S. J., Schell, M. A., and Denny, T. P. (1997) Mol. Microbiol. 26, 251-259). Therefore, as Ralstonia solanacearum invades into crops and grows therein, the concentration of the compound increases, thereby developing pathogenicity.
Accordingly, the above-mentioned compound is expected to be used as a precursor for developing agricultural chemicals that are effective to bacterial wilt. The enzyme activity to decompose the compound is supposed to be applicable to a new breeding method for restraining the bacterial wilt.
However, only a chemical method such as an alkaline hydrolysis used for general fatty acid esters has been available as a reaction of decomposing the compound, for example, a method of hydrolyzing the compound into 3-hydroxypalmitic acid and methanol, represented by the general formula (II)
Therefore, the reaction must have been performed under strong reaction conditions, including, for example, use of a strong alkali.
If an enzyme activity that catalyzes this reaction is found, hydrolysis of methyl 3-hydroxypalmitate can be carried out under mild reaction conditions unlike the chemical methods. In addition, even if other fatty acids coexist, use of an appropriate enzyme activity enables selective hydrolysis of methyl 3-hydroxypalmitate utilizing substrate specificity of the enzyme. However, no reports on the enzyme activity to hydrolyze methyl 3-hydroxypalmitate have been available.
Accordingly, it is an object of the present invention to provide an enzyme that hydrolyzes methyl 3-hydroxypalmitate, a microorganism that produces the enzyme, and a method of producing the enzyme.
The inventors of the present invention have made extensive studies with a view to achieving the above-mentioned object, and as a result, they have found that a microorganism isolated from soil has an ability to produce the above-mentioned enzyme, esterase; the present invention has been completed based on this finding.